Cytomegalovirus (CMV) infections following renal transplantation are extremely common, occurring in 60-86% of patients studied. This proposal seeks: (1) to establish more firmly the relationship between CMV and hepatic function abnormalities occuring in the post-transplant period and to determine the spectrum and natural history of hepatitis associated with CMV seroconversion, (2) to explore the possibility that CMV infection may be an important cause of graft rejection, (3) to initiate in vitro experiments designed to gain information on how certain epidemiologically significant variables (hydrocortisone, azathioprine, uremia, and antigenic stimulation) might influence CMV replication and the immune response to this infection, (4) to determine whether the "immunological enhancement of viral replication" extends to CMV, and (5) to ascertain the relative contribution of viral multiplication versus the immune response in the causation of cellular injury and death. To achieve these objectives we will study prospectively 50 patients undergoing renal transplantation and set up experiments utilizing human fibroblasts and mononuclear cells, CMV and relevant variables, measuring the results in terms of viable cells remaining at the end of the experiment and virus yield.